Conventionally, there has been generally known a method wherein an LCD and a flexible board (flexible wiring board) mounted with, by the use of bonding wires, an LCD driver IC for controlling driving and display of the LCD are electrically and mechanically connected together by bonding, with thermal pressurization, the flexible board to a terminal portion of the LCD by the use of heat sealing or an ACF (anti-conductive film).
There is one wherein, in order to mount a flexible board on a printed circuit board, the flexible board is bent downward of an LCD near a connecting portion between the LCD and the flexible board so as to be folded double, thereby mounting the flexible board between an LCD frame and the printed circuit board.
A flexible board in prior art 1 comprises an elongated base board, a plurality of wiring patterns formed on the base board, and a plurality of reinforcing portions formed on the base board. The plurality of reinforcing portions are disposed so as to extend in a longitudinal direction of the base board. Part of the wiring patterns are formed at positions offset from the respective reinforcing portions in a width direction of the base board.
Since a portion of the base board where the reinforcing portion is formed is more reluctant to bend than a portion where the reinforcing portion is not formed, bending stress is concentrated at the portion where the reinforcing portion is not formed. Part of the wiring patterns are formed at positions offset from the reinforcing portions in an axial direction of the base board. When the base board is rolled up, since portions where at least part of the wiring patterns are formed are reluctant to bend due to the reinforcing portions, it is possible to prevent deformation of the wiring patterns [see, e.g. Republished Patent International Publication No. WO0054324 (patent document 1)].
On the other hand, in prior art 2, there is a portable telephone LCD holding structure comprising an LCD, a printed circuit board mounted with various electrical circuits, a flexible board having an LCD drive circuit and mounted on the printed circuit board so as to be electrically connected thereto through the LCD and a bending portion, and a frame member holding the LCD on its upper surface and supported by the printed circuit board, wherein assembling is made by folding the bending portion continuous with the flexible board so that the LCD, the frame member, the flexible board, and the printed circuit board are disposed in the order named from above [see, e.g. Japanese Patent No. 3110408 (patent document 2)].
Further, in prior art 3, there is a multilayer wiring board comprising a flexible bending portion, wiring layers forming the bending portion, and a flat portion having more wiring layers than the bending portion, wherein a boundary portion is provided between the flat portion and the bending portion, in which the number of wiring layers is reduced stepwise as compared with the flat portion.
In this multilayer wiring board, stress concentration is relaxed at the boundary portion between the flat portion and the bending portion of the wiring board having the bending portion, thereby preventing failure such as breakage of the board or cutting of wiring patterns [see, e.g. Japanese Unexamined Patent Application Publication No. 2000-223835 (patent document 3)].
However, in prior art 1 or 2, since a technique is adopted to improve bending resistance by performing additional processing such as shaving thinly the portion subjected to bending to increase flexibility and unifying a reinforcing plate, the additional processing is required to cause an increase in cost. Further, there is a problem that sufficient resistance cannot be obtained even by taking such a measure.
As a cause therefor, there is a problem in terms of a material such that use is made of copper having high conductivity as a metal for use and the copper has a narrow elastic range and easily gives rise to stress movement in repetitive bending.
Further, in prior art 1 or 2, there is a problem that since it is difficult to accurately dispose wiring due to processing variation, the resistance is reduced due to subjection to stress.
Generally, a base material provided with a wiring pattern is often a polyimide resin and therefore the intrinsic problem has not been solved that since the polyimide resin is a hard resin having elasticity, stress concentration is liable to occur so that the resistance is degraded due to buckling or excessive deformation caused by bending.
Further, in prior art 3, a base material provided with the wiring patterns is a polyimide resin and additional processing is required.
It is therefore an object of this invention to provide an electrical connection component that can improve the bending resistance.